Women travelling home alone are being urged to use only minicabs they have booked, after three were assaulted in west London.
Metropolitan Police said the attacks took place in the Clapham and Putney areas on three mornings in August.
Once the women were in the vehicle, the man stopped the car and assaulted them, a spokesperson for the force said.
Although none of the women sustained serious injuries they were left “traumatised”, the officer added.
The assaults took place in Battersea Rise on 3 August at 01:55 BST, and in Putney High Street on 11 August at 00:10 and 18 August at 02:47.
Det Insp Joanne Flynn, of the South West Command Unit’s CID, said: “We are following a number of lines of inquiry, however, it is important that we make women aware that this predatory man is out there.
“Although none of the victims sustained serious injuries, they were, understandably, traumatised by the incidents.”
Det Insp Flynn added the vehicle “may or may not be a genuine minicab” and therefore it was important, that where possible, people booked cabs in advance and ideally “don’t travel home alone”.
Anyone who thinks they may have encountered the man or has any information about the attacks, is asked to contact the Metropolitan Police.